build: Bump symfony/mailgun-mailer from 7.1.3 to 7.1.6

Bumps [symfony/mailgun-mailer](https://github.com/symfony/mailgun-mailer) from 7.1.3 to 7.1.6.
- [Release notes](https://github.com/symfony/mailgun-mailer/releases)
- [Changelog](https://github.com/symfony/mailgun-mailer/blob/7.1/CHANGELOG.md)
- [Commits](symfony/mailgun-mailer@v7.1.3...v7.1.6)

---
updated-dependencies:
- dependency-name: symfony/mailgun-mailer
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>